This application is related to Japanese Patent Application No. HEI 11(1999)-183650 filed on Jun. 29, 1999,, whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to methods for testing and for controlling a coating liquid for an electrophotographic photoconductor, especially, an organic electrophotographic photoconductor, and a method of producing an electrophotographic photoconductor using the test and control methods.
2. Description of Related Art
Recently, in the fields of electrophotographic photoconductors (referred to just as xe2x80x9cphotoconductorsxe2x80x9d hereinafter) used in image forming apparatuses such as copying machines and laser printers, the development of organic photoconductive materials have made a remarkably progress and have become more widely in use than inorganic photoconductive materials which have been used. The photoconductors using organic photoconductive materials have some disadvantages in sensitivity, durability and stability to environment, but are much more advantageous than the inorganic photoconductive materials in toxicity, production costs, degree of freedom in material designing and the like. Now a variety of sensitizing methods are proposed.
Particularly, laminated photoconductors comprised of a charge generation layer and a charge transport layer exhibit an excellent sensitizing property and account for a majority of organic photoconductors currently in practical use. The laminated photoconductors are expected to be the mainstream photoconductors in the future.
In the laminated photoconductors, the charge generation layer contains a charge generation material which generates a charge carrier when irradiated with light, and the charge transport layer contains a charge transport material which receives and transports the charge carrier generated in the charge generation layer.
An undercoating layer is also provided on an electroconductive support with the intention of improving electrification characteristics, preventing unnecessary injection of charges from the electroconductive support, covering defects on the electroconductive support, preventing generation of pinholes, improvement adhesion of photoconductive layers (i.e., the electroconductive support and charge generation layer) and the like. Thus, the durability of photoconductors has been improved.
To produce a laminated photoconductor, organic photoconductive materials for constituting the respective photoconductive layers, together with binding resins, are dissolved or dispersed in organic solvents to prepare coating liquids for the photoconductor (referred to as xe2x80x9ccoating liquidsxe2x80x9d hereinafter), which are sequentially applied on an electroconductive support and dried.
Since these coating liquids are continuously used by being circulated in an apparatus for a long time or are used after being stored for a considerably long time, the composition and/or viscosity of the coating liquids often change due to natural vaporization of organic solvents. Such change is remarked particularly in the case where a mixed solvent of two or more solvents is used.
FIG. 3 illustrates an example of an apparatus for producing photoconductors, in which a coating liquid is circulated in a path formed by a coating vessel 6, an overflow liquid receiver 11, a recycling tube 12, an agitating vessel 7 provided with an agitator 13, a circulating pump 9, a filter 10, a circulating tube 8, and back to the coating vessel 6. The filter is provided for removing agglomerates of the coating liquid and dust generated in the apparatus. If the filter is used over a long time and the coating liquid contains a pigment dispersed as an organic photoconductive material, the filter catches agglomerates or gels of the pigment. As a result, the proportion of the pigment in the coating liquid changes.
Besides, the undercoating layer is often formed of a polyamide resin, and a hydrophilic organic solvent is used in consideration of the solubility of the polyamide resin. The hydrophilic organic solvent is easily mixed with water and it can hardly be grasped how much water has mixed in a coating liquid for the undercoating layer.
If a photoconductor is produced with use of a coating liquid whose composition has changed or has become ununiform and/or into which water has mixed, there possibly occur a decline in the film forming property of the coating liquid, defect in formed images and deterioration in electrophotograpic characteristics such as sensitivity. For example, if a photoconductor is produced with use of a coating liquid for the undercoating layer into which water has mixed and then the photoconductor is mounted in an image forming apparatus performing reverse development, small dark spots appear in white blank images.
Further, variation in the composition of the coating liquids among production lots may adversely affect characteristics of the photoconductors in the same manner as described above.
When the variation or ununiformity in composition, contamination of water or variation among production lots takes place in the coating liquids as described above, it is common to measure viscosity, clearness and particle distribution of the coating liquids and, according to the measurement results, add an insufficient component or judge that the coating liquids are out of use. In the apparatus of FIG. 3, the viscosity of the coating liquids is measured by a viscometer provided in the agitating vessel 7, and according to the measurement result, a solvent is added by an solvent supplementing device 16.
In addition to the measurement of the viscosity, some other means have been proposed for detecting change of the coating liquids with time.
For example, Japanese Unexamined Patent Publication No. HEI 10(1998)-48851 has disclosed a method of testing a coating liquid for a charge generation layer employing thermogravimetry for obtaining the proportion of a charge generation material to a binding resin, Japanese Unexamined Patent Publication No. HEI 3(1991)-17556 has disclosed a method of testing a photoconductor coating liquid employing a thin-layer chromatographic test method, and Japanese Unexamined Patent Publication No. HEI 4(1992)-67153 has disclosed a method of testing a photoconductor coating liquid employing absorption spectra by spectrophotometric analysis.
However, the above-mentioned method using the thermogravimetry requires a pre-treatment of evaporating an organic solvent in the coating liquid for the charge generation layer to dry and solidify the coating liquid, and in this pre-treatment, impurities may mix in the coating liquid. Moreover, since the organic solvent is removed by evaporation, the ratio of other components to the organic solvent cannot be obtained and the content of water cannot be quantitatively evaluated.
The method employing the thin-layer chromatographic test method can be used only for evaluating the dispersion state of a coating liquid containing a pigment. The method employing the absorption spectra can be used only for evaluating the dispersion state of a charge generation material.
Under these circumstances, an object of the present invention is to provide a test method for a coating liquid capable of effectively determining the ratio and/or content of a component to be analyzed in the coating liquid with good accuracy without contamination by impurities.
The present invention provides a test method for a coating liquid for a photoconductor comprising: calculating a peak area ratio of a component to be analyzed in a coating liquid by pyrolysis gas chromatography, and comparing the peak area ratio with a pre-calculated peak area ratio of the component in a reference coating liquid having a known content of the component, to determine the ratio and/or content of the component in the coating liquid.
The present invention also provides a control method for controlling a coating liquid for a photoconductor comprising: determining the ratio and/or content of a component to be analyzed in a coating liquid for a photoconductor by the above-described test method; and on the basis of the obtained result, adjusting the coating liquid so that its composition is constant or newly preparing the coating liquid, thereby to control the quality of the coating liquid.
The present invention further provides a production method of a photoconductor characterized by producing a photoconductor using a coating liquid therefor controlled by the above-described control method.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.